Purpose :
The goal of the research in the laboratory is to characterize proteins that are required for normal retinal function, and in particular those containing leucine rich repeats (LRR). Proteins containing these domains have been targeted because two such genes, Nyctalopin and LRIT3, contain LRRs, and mutations in these genes lead to the complete form of congential stationary night blindness because they are critical to depolarizing bipolar cell function. Because large numbers of such proteins are expressed in the retina we hypothesize others will have similar function.

Methods :
We are using CRISPR/Cas9 screens to create mouse mutants lacking multiple LRR proteins. gRNAs that target multiple genes are injected into mouse embryos, and the founders are bred. After appropriate crosses are made, we identify mutant mice of interest using the ERG. In each mouse line that has an abnormal ERG we examine overall retinal structure, and the localization of DBC synaptic components including the markers PNA, pikachurin, ribeye, GPR179, and cone arrestin (mCAR).

Results :
We have identified a mouse line that has a normal scotopic ERG, but lacks photopic a- and b-waves. This suggests either non-functional cones or a complete absence of cones. We examined this by staining for the cone outer segment and synaptic marker PNA and mCAR. The results showed that the gross morphology of the retina is normal and that cones are present in normal numbers. We also examined expression of the DBC synaptic markers pikachurin and ribeye. All showed a pattern indistinguishable from that in littermates that had a normal ERG.

Conclusions :
The experiments have identified a new no-cone ERG mutant mouse line that has normal cone morphology. Current efforts are focused on using genetic and next-generation sequencing strategies to identify the causative mutation.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.